In my earlier post, I was asking if the sound from the dock port is untouched, because the eq settings are still in effect, and stv014 replied that line-out from dock skips the internal headphone amp, but it does not skip DSP, which puts the eq effect. Thanks for the answer, which is correct I think.
Now, I am trying to figure out more about the sound output of iphone from the dock port.
I am connecting my phone to a Sony micro hifi system "CMT-G1IP", which does not have a dock station but a standard USB port instead. From the USB port, system can read flash disks and play audio files, and it can also play music from iphones and ipods. (I use the standard data cable of iphone for connecting to the system)
From what I read so far, I think there is another component, which is DAC in between iphone DSP and the internal headphone amp.
So, the sound path througn the headphone jack is like:
"RAW DATA" -> DSP -> DAC -> Internal Headphone amp.
Ok, receiving the sound via the dock port line out ensures that the sound is not processed by the "Internal headphone amp."
Now, I want to know if my system is receiving audio signal in digital or analog format. Is the internal DAC of iphone used or not?
Iphone and Ipods can deliver either digital or analog audio via the 30 pin dock port. And many docking speakers use the analog output.
I have looked at the pinout diagram of Apple 30 pin connector. From there, I saw that pins 3 and 4 are used for analog audio output for left/right channels respectively. Additionally, pin 2 is used for ground signal. That makes totally 3 pins for the audio only.
And, additionally, this micro hifi system also charges the iphone through the usb port, which must then be using pins 16 and 23, which are for 5V and Ground. Adding these 2 pins, device totally needs 5 pins.
Finally, hifi system can also control the ipod, so that you can play/pause/etc.. And that signal is carried by other 2 pins.
So totally, 7, out of 30 pins must be used, if my system was receiving the audio in analog format.
But, USB bus only has 4 pins. 5V, Data Tx, Data Rx and Ground. So, you would not have enough pins if you wanted to carry the audio signal in analog format.
...And this makes me believe that all devices which transmit audio from ipod/iphone by using a "USB cable", must transmit the audio in digital format.
And for the systems receiving the audio direcly by docking the device using the dock port, it depends on the receiver system. It can be analog or digital.
Am I true, or am I missing something here?
Any answers are welcome.
Note: By the way, analog output from the dock port is no more offered in iPhone 5 lightning port. Because of this, Apple had to put DAC into the lightning to 30-pin dock port adapter.
So, I can find an iPhone 5 and try if it works with my system, I will be sure that audio is indeed transferred digitally. May be someone who has the latest iPhone can try a similar test??
Edited by alperkocatas - 10/14/12 at 9:55am